sys/net/lorawan: fix cpp namespace
sys/net/lorawan: fix cpp namespace

ant9000/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,authmillenon/RIOT,kYc0o/RIOT,authmillenon/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,kYc0o/RIOT,authmillenon/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,OlegHahm/RIOT,miri64/RIOT,authmillenon/RIOT,ant9000/RIOT,authmillenon/RIOT,ant9000/RIOT,kaspar030/RIOT,kaspar030/RIOT,ant9000/RIOT,kYc0o/RIOT,OlegHahm/RIOT,miri64/RIOT,jasonatran/RIOT,kYc0o/RIOT,OlegHahm/RIOT,kaspar030/RIOT,kaspar030/RIOT,ant9000/RIOT,jasonatran/RIOT,OTAkeys/RIOT,jasonatran/RIOT,miri64/RIOT,miri64/RIOT,RIOT-OS/RIOT,miri64/RIOT,OlegHahm/RIOT,authmillenon/RIOT,jasonatran/RIOT